The gangbangers will act like gangbangers until a few of them are shot down by the larger community which is no longer constrained by regulations on the use of deadly force. Gangbangers aren't the only ones who can organize, and there are lot more of us than there are of them.
My coworker lives in a "larger community" that couldn't defend itself from a rabid mouse. None of them have firearms, ammo or skill to use them. After TSHTF it will be too late to acquire those. That's exactly the point of preppers. You cannot defer to some "larger community" - it will be in the same boat as you are.
I'm living in a semi-rural area, and all my neighbors are well equipped to defend the only road that goes here. But from my home I can see a huge expanse of those "larger communities" in the city that will fall prey to a single coyote, let alone a hundred well-armed and physically fit gang members.
I wouldn't give too much weight to the fear factor. Stupid people (who make the majority in a gang) always think that bad things happen only to someone else. If a hundred of them attacks you and you eliminate two, do you think the remaining 98 will run away in fear? "He killed Kenny, get him!1!" and then they rush you. Attackers on drugs (a.k.a. berserkers) are even unable to understand what is happening. Such a gang has to be wiped out nearly completely to be neutralized. A couple of them shot will only result in retaliation - because a gang cannot afford such a disrespect, it lowers its standing. Besides, the gang leaders who order the attack aren't going to lead it. Gang soldiers are expendable. A collapsed society is a rich source of cannon fodder; people will be dirt cheap, many will fight and die only for a daily can of food.
If your "larger community" kills gang members it better be willing to take on the entire gang and win. However most communities in cities are randomly organized. You may get one soldier, one accountant, one nurse, one philosopher, and one artist. You will be against 100 professional killers. What are your chances?
This scenario unfolded many times in human history, when an organized attacker conquered hundreds of tiny, unorganized settlements. Genghiz Khan is the most famous, of course, but he is not the only one. Your "larger community" has to be large enough to be strong enough - or it has to be extremely well prepared. Which is exactly what people are discussing here.